Refining of wood pulp



U d States Patent 1 2,789,902 REFINING F woon PULP 5' to the refining ofwood pulp and ,Xelates more particularly to an improved process for therefill fllg df- W0 o d pulp which will reduce the resin content of saidwood pulp to an extremely low value.

In the production of chemical wood pulp suitable for small proportion ofthe non-cellulosic materials present .therein. During such treatment,-it is important to minimize the degradation of the cellulosic materialsince such degradation would reduce the alpha cellulose 'content and pthe viscosity of the final product to undesirably low values.

'To avoid 'an excessive degree of degradation of the pulp,

the treatments to which said pulp is subjected must be relatively mild.However, mild treatments make it difficult to obtain a satisfactorydegree of refining of the wood pulp. This represents an especiallydifiicult problem in the production of acetylation grade wood pulp thatis employed for the manufacture of cellulose acetate and other organicacid esters of cellulose since such pulp must have a high alphacellulose content and a high viscosity, together with an extremely lowcontent of non-cellulosic impurities.

It is an important object of this invention to provide an improvedprocess for the refining of wood pulp which will overcome at least inpart the foregoing and other difiiculties.

A further object of this invention is to provide an improved process forthe refining of wood pulp which will reduce the resin content of saidpulp to an extremely low value.

Other objects of this invention will be apparent from the followingdetailed description and claims.

According to the present invention, a digested wood pulp is subjected asone stage in its refining to a hot alkali boil in the presence of anon-ionic detergent, comprising a polyglycol ether of an alkyl phenol,and tall oil. It has been found that the treatment of the wood pulp inthis manner reduces its resin content to an extremely low value without,however, causing an excessive reduction in the alpha cellulose contentof the wood pulp or in the viscosity thereof. The product obtained iswell suited for use as an acetylation grade wood pulp. The efiectivenessof the non-ionic detergent mixed with the tall oil is quite surprisingsince it reduces the resin content of the wood pulp to values of fromone-fifth to one-half of that obtained when the detergent is used alone,yet tall oil itself has little or no effect on the resin content of thewood pulp.

In carrying out this process, the digested wood pulp, which'mayadvantageously be a sulfite wood pulp, may be treated first withchlorine and also with a bleaching agent such as a hyp-ochlorite, in amanner well known in the art. Following these initial treatments, thewood pulp is subjected to an alkali boil. For the alkali boil theconsistency of the wood pulp is adjusted to between about 2. and 20% byweight and the concentration of sodium hydroxide to between 3 and 25% byweight on the weight .tion further.

of the bone dry pulp. There are present in the wood pulp slurry duringthe alkali boil from about 0.1 to 1% by weight on the Weight of the bonedry pulp of the nonionic detergent and from about 0.1 to 5% by weight onthe weight of the bone dry pulp of tall oil. The alkali boil is carriedout at a temperature of between about and 170 C. and for a period ofbetween about 10 and 240 minutes. Following the alkali boil the woodpulp is drained and washed and may be treated with bleaching agents suchas hypochlorite, chlorine dioxide and the like further to improve itsproperties.

The non-ionic detergent used in carrying out this invention comprises apolyglycol ether of an alkyl phenol in which the alkyl group containsfrom about 4 to 20 or preferably from about 6 to 15 carbon atoms. Thepolyglycol with which the alkyl phenol is etherified contains from about6 to 20 or preferably from about 8 to 15 recurring units in its chain,which units may be derived from ethylene oxide, propylene oxide,butylene oxide and the like. The preparation of these non-ionicdetergents is fully described in U. 5. Patent No. 2,213,477. The talloil which is present during the alkali boil is a by-product derived fromthe digestion of wood pulp by the sulfate process and is a mixture ofrosin acids and fatty acids with minor quantities of sterols and thelike.

The following example is given to illustrate this inven- Example Asulfite wood pulp which has been chlorinated and washed is diluted withan aqueous sodium hydroxide solution to a consistency of 8% by weight,the sodium hydroxide content of the diluting solution being selected tobring the sodium hydroxide concentration of the slurry to 12% by weighton the weight of the bone dry pulp. There is incorporated into the woodpulp slurry 0.3% by weight on the weight of the bone dry pulp of themixed ether made by condensing monyl phenol with about 10 moles ofethylene oxide for each mole of the phenol and about 1% by weight on theweight of the bone dry pulp of a tall oil having an acid number of 186to 191, and including from 66 to 71% by weight of fatty acids, 25 to 30%by weight of rosin acids and 2 to 4% by Weight of sterols and the like.The slurry is charged into a pressure vessel and heated over a period of25 minutes to a temperature of C. and is held at this temperature for anadditional 20 minutes. The wood pulp is then washed and soured to a pHof 5.5 with sulfur dioxide water.

The alcohol-benzene solubles in the wood pulp, which is a measure of theresin remaining in the pulp, are only 0.030% by weight on the weight ofthe bone dry pulp. The alpha cellulose content of the purified wood pulpand the viscosity thereof are high, so that after bleaching withhypochlorite the product obtained is suitable for use as an acetylationgrade pulp.

In the appended claims the weight of the wood pulp is on a bone drybasis.

It is to be understood that the foregoing detailed description is givenmerely by way of illustration and that many variations may be madetherein without departing from the spirit of our invention.

Having described our invention, what we desire to secure by LettersPatent is:

1. In a process for the purification of wood pulp, the step whichcomprises subjecting the pulp to a hot caustic boil in the presence oftall oil and a polyglycol ether of an alkyl phenol.

2. In a process for the purification of wood pulp, the step whichcomprises subjecting the pulp to a hot caustic boil at a temperature ofbetween about 80 and C. for a period of between about 10 and 240 minutesin the presence of tall oil and a polyglycol ether of an alkyl phenol.

boil at a consistency of between about 2 and 20% by weight and a causticconcentration of between about 3 and 25% by weight on the weight of thepulp in the presence of tall oil and a polygiycol ether or an alkylphenol.

4. In a process for the purification of wood pulp, the step whichcomprises subjecting the pulp to a hot caustic ,boil in the presence offrom about 0.1 to 1% by weight on'the weight of the pulp of a polyglycolether of an alkyl phenol and from about 0.1 to by weight on the weightof the pulp of tall oil.

5.- In a process for the purification of wood pulp, the step whichcomprises subjecting the pulp to a hot caustic boil at a temperature ofbetween about 80 and 170 C. for a period of between about and 240 hoursat a consistency of between about 2 and 20% by weight and a causticconcentration of between about 3 and 25% by weight on the weight of thepulp in the presence of from about 0.1 to 1% on the weight of the pulpof a polyglycol ether of an alkyl phenol and from about 0.1 to 5% byweight on the weight of the pulp of tall oil.

6. In a process for the purification of wood pulp, the steps whichcomprise forming a wood pulp slurry containing sodium hydroxide, addingtall oil and a poly- IgIyool ether of an alkyl phenol to said wood pulpslurry, and subjecting said Wood pulp slurry to elevated temperature.

7. In a process for the purification of wood pulp, the steps whichcomprise forming a wood pulp slurry containing sodium hydroxide, addingto said wood pulp slurry from 0.1 to 5% by weight on the weight of thepulp of 4 tall oil and from 0.1 to 1% by weight on the weight of thepulp of a polyglycol ether of an alkyl phenol, and subjecting said woodpulp slurry to elevated temperature.

8. In a process for the purification of wood pulp, the steps whichcomprise forming a wood pulp slurry containing sodium hydroxide in aconcentration of between about 3 and 25% by weight on the weight of thepulp, adding to said wood pulp slurry from 0.1 to 5% by weight on theweight of the pulp of tall oil and from 0.1 to 1% by weight on theweight of the pulp of a polyglycol ether of an alkyl phenol, andsubjecting said wood pulp slurry to a temperature of between about to C.for a period of between about 10 and 240 minutes.

References Cited in the file of this patent UNITED STATES PATENTS1,833,976 Richter et a1 Dec. 1, 1931 1,847,311 Schur et a1 Mar. 1, 19322,128,928 Estes Sept. 6, 1938 2,213,477 Steindorff et al Sept. 3, 19402,596,092 Bonneville May 13, 1952 FOREIGN PATENTS 740,664 Germany Mar.31, 1944 OTHER REFERENCES Printing Inks, by Ellis, p. 482, published byReinhold Pub. Corp., New York (1940).

Deinking of Waste Paper, by West, pp. 8 and 9, published by Institute ofPaper Chemistry, Appleton, Wis. (1943).

1. IN A PROCESS FOR THE PURIFICATION OF WOOD PULP, THE STEP WHICHCOMPRISES SUBJECTING THE PULP TO A HOT CAUSTIC BOIL IN THE PRESENCE OFTALL OIL AND A POLYGLYCOL ETHER OF AN ALKYL PHENOL.